1. Field of the Invention
The invention relates to IGFET circuits and to analog to digital converters, and more particularly to IGFET analog to digital converters which may be implemented on a semiconductor chip.
2. Description of the Prior Art
MOS technology has been utilized recently to implement a wide variety of complex electronic functions on semiconductor chips. In particular, extremely complex memory and digital logic functions have been implemented on single semiconductor substrates utilizing MOS technology, and to a lesser extent linear circuits have also been implemented thereby. Although digital to analog converters have been available for some time, most applications for electronic digital to analog converter circuits require use of precision value discrete components. For example, many digital to analog converters utilize precision resistor ladder networks or networks of precision constant current sources. With present tolerances associated with the manufacture of MOSFET integrated circuit devices, there is a wide tolerance variation in individual MOSFET characteristics. This wide tolerance variation is in direct conflict with the precision device characteristics required by many prior approaches to digital to analog conversion. Although some digital to analog converters have been implemented on a semiconductor chip utilizing MOSFET technology, the designs have not been suitable for producing the degree of accuracy required in many applications.